This disclosure relates to thermoplastic polyester compositions, methods of manufacture, and articles thereof.
Thermoplastic polyesters, such as poly(alkylene terephthalate)s, are readily molded into useful articles, and articles comprising thermoplastic polyesters have valuable characteristics including strength, toughness, high gloss, and solvent resistance. Thermoplastic polyesters therefore have utility for a wide range of applications, including automotive parts, electric appliances, and electronic devices. Because of their widespread use, particularly in electronic applications, it is desirable to provide flame retardance to thermoplastic polyesters.
Numerous flame retardants (FR) for thermoplastic polyesters are known, but many contain halogens, usually chlorine and/or bromine. Halogenated flame retardant agents are undesirable because of the increasing demand for ecologically friendly materials. Articles comprising halogenated flame retardants emit toxic and corrosive hydrochloric acid and/or hydrobromic acid when burned, and pose a water and/or soil pollution hazard when disposed of in the environment. Halogen-free flame retardants, such as phosphorus- and nitrogen-based compounds are known. However there is a need to improve the flame retardance of thin molded articles containing phosphorus- and nitrogen-based flame retardants.
More ecologically friendly FR (eco-FR) thermoplastic polymer compositions comprising aluminum phosphinate or diphosphinate and melamine compounds have been developed to replace compositions comprising halogenated flame retardants. However, these eco-FR compositions possess poor mechanical properties, including reduced impact strength and tensile strength, as well as poor flow properties compared to compositions having halogenated flame retardants. The addition of small amounts of a polyetherimide (PEI), in particular ULTEM 1010 from SABIC Innovative Plastics, can boost the mechanical properties of the eco-FR compositions. However, PEI lowers the comparative tracking index (CTI) compared to halogenated frame retardants, i.e. it increases the tendency to form conductive leakage paths on the surface of the molded article.
Thus, there remains a need for eco-FR thermoplastic polyester compositions having good flame retardant properties when molded into thin sections, and at the same time having comparable or improved mechanical properties, including ductility, tensile strength, and stiffness relative to compositions comprising halogenated flame retardants.